Ligands TolBINAP

Metal-catalyzed C-H bond formation through isomerization, especially asymmetric variant of that, is highly useful in organic synthesis. The most successful example is no doubt the enantioselective isomerization of allylamines catalyzed by Rh(i)/TolBINAP complex, which was applied to the industrial synthesis of (—)-menthol. A highly enantioselective isomerization of allylic alcohols was also developed using Rh(l)/phosphaferrocene complex. Despite these successful examples, an enantioselective isomerization of unfunctionalized alkenes and metal-catalyzed isomerization of acetylenic triple bonds has not been extensively studied. Future developments of new catalysts and ligands for these reactions will enhance the synthetic utility of the metal-catalyzed isomerization reaction. 

Ir(cod)Cl]2> reactions afforded enantiomerically enriched cyclopentenones when (S)-tolBINAP was employed as ligand. The corresponding cyclopentenones were obtained in yields up to 85% and ee values ranging from 82 to 98%. Interestingly, Co2(CO)8 in combination with a chiral bisphosphite also gives access to chiral Pauson-Khand products [66]. Here, yields were observed up to 97% however, in most cases the ee was rather low (< 20%). Equation 11 summarizes some representative examples of enantioselective PKR. 

The excellent catalytic activity is rationalized by a nonclassical metal-ligand bifunctional mechanism using an NH effect. As shown in Figure 1.18, frani-RuH(ri -BH4)(tolbinap)(dpen) (18A) (TolBINAP see Figure 1.2), a precata-... 

Figure 1.19. (5)-TolBINAP/(5,5 )-DPEN-RuH2 species and diastereomeric transition states in the metal-ligand bifunctional catalysis the equatorially oriented phenyl substituents in the DPEN ligands are omitted in the transition states 5 -19A and Re-19A (Ar = 4-CH3C6H4 O = Ru ax = axial, eq = equatorial).

Enantioselective carbonylative cyclization has been realized with o-alkenylaryl triflates in the presence of 2,2-bis(diphenyl-phosphanyl)-1,1-binaphthyl (BINAP) or TolBINAP ligands in high material yields and enantiomeric excess (Equation (41)). ... 

Besides BINAP or p-TolBINAP, optically active peraryldiphosphines with axial chirality based on the biphenyl groups (6,6 -dimethylbiphenyl-2,2 -diyl)bis(diphenylphosphine) and its analog are also effective ligands for the asymmetric isomerization as expected [21],... 

Asymmetric cycloaddition of 2-vinyloxiranes to carbodiimides proceeds in the presence of Pd2(dba)3-CHC13 and TolBINAP as the chiral ligand in THF at room temperature to yield 4-vinyl-l,3-oxazolidin-2-imines with up to 95% ee [74] (Eq. 8A.50). The enantio-determining step is assumed to be the nucleophilic attack of a nitrogen nucleophile on a 7i-allylpalladium intermediate. Reactions of 2-vinyloxiranes with isocyanates using the same catalyst system afford 4-vinyl-l,3-oxazolidin-2-ones with low enantioselectivity. 

For BPPFA, CHIRAPHOS, DIOP, TolBINAP, and NORPHOS, see the Ligand list for Chapter 1. 

Cationic rhodium(I) complexes catalyze the isomerization of tertiary ally-lamines E-11.17 and Z-11.17 to enamines 11.18. In THF at 80°C, these enamines are readily hydrolyzed to provide aldehydes. When the rhodium ligand is a chiral diphosphine such as (R)- or (6)-binap 3.43 (Ar = Ph), or better yet, (R)- or (S)-tolbinap 3.43 (Ar = 4-MeC6H4), (R) or (5)-enamines 11.18 are obtained with an excellent enantiomeric excess. This method is used in industry for the synthesis of optically active dtronellol and menthol [811, 812, 853, 889], Biphemp 3.45 is also a highly potent ligand for the isomerization of Z-11.17, and ee s as high as 99.5% are observed [905]. The absolute configuration of the enatnine product... 

The allyl alcohol (2.84) could be hydrogenated with exceptionally high diastere-oselectivity using ruthenium/(J )-TolBINAP complexes. The substrate diastere-oselectivity and catalyst selectivity represent a matched pair, since, when the enantiomeric (S)-TolBINAP ligand was used, the opposite diastereomer was formed with only 56% de. 

Elimination in some cyclic systems proceeds regio- and stereoselectively. The Pd-catalyzed reaction of the racemic carbonate 491 afforded the diene 492 with 86 % ee via desymmetrization of the 7r-allylpalladium intermediate 493 when (-)-TolBINAP was used as a ligand [190],... 

Shibata and co-workers found cinnamaldehyde to be the most efficient aldehyde in a solvent-free system. Using [Rh(dppp)2Cl] (5 mol%) as catalyst, commonly used enynes were converted to the cyclopentenones in high yields. Perhaps more encouraging is that a preliminary experiment under asymmetric conditions using tolBINAP as a chiral ligand gave the cycloadduct product 180 in 89% yield and 83% ee (Scheme 82). 

Ooka, H. Aral, N. Azuma, K. Kurono, N. Ohkuma, T. Asymmetric hydrogenation of aromatic ketones catalyzed by the TolBINAP/ DMAPEN-Ruthenium(II) complex A significant effect of N-substituents of chiral 1,2-diamine ligands on enantioselectivity. /. Org. Chem. 2008, 73, 9084-9093. 

Finally, enantioselective cycloisomerizations of 1,6-enynes 45 have been reported using an iridium catalyst in the presence of tolBinap as the chiral ligand, leading to the expected aza-bicyclo[4.1.0]heptane derivatives 46 in good yields but moderate (up to 78%) enantioselectivities (Scheme 5.16) [66],... 

For example, access to axial chirality can be realized under cobalt catalysis using a chiral cobalt(I) complex [4], However, the use of chiral iridium and rhodium species dramatically improved the scope and enantioselectivities obtained for this cycloaddition. Tanaka and coworkers synthesized an atropoisomeric diphosphine oxide in 97% ee, by treatment of the suitable hexayne with [Rh(cod)2]BF4 in the presence of (7 )-TolBINAP as source of chirality (double [2-1-2-1-2] cycloaddition). Subsequent reduction afforded an axially chiral bidentate ligand as a single enantiomer (Scheme 7.1) [5]. 

Asymmetric versions of these reactions have been carried out by Tanaka [49] and Shibata [50] by using rhodium complexes of modified BlNAPs (Fig. 10.37). TolBinap and Hg-Binap were found to be appropriate chiral ligands for the cycloadditions of enynes with oxygen, carbon or nitrogen tethers. In the case of nitrogen-tethered substrates, the substituent of the alkyne unit has a crucial effect... 

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